The invention relates to a radiometric detector for detecting a measurement variable.
Radiometric measurement systems, which comprise scintillation detectors for measuring radiation, are used in process metrology for measuring a measurement variable or a process variable such as e.g. a filling level, a moisture, a density, a mass flow, etc. By way of example, the scintillation detectors serve to determine the energy and/or intensity of ionizing radiation, wherein the energy and/or the intensity of the ionizing radiation depend(s) on the measurement variable.
In addition to the accuracy of the measurement of the measurement variable, a high availability of the measurement is important in process metrology. The absence of a measurement can lead to significant costs for the operator; in particular, damage to objects and persons may be the consequence in safety-critical installations.
The invention is based on the object of providing a radiometric detector for detecting a measurement variable, which detector is particularly failsafe while, simultaneously, having a simple design.
The invention achieves this object by the provision of a radiometric detector for detecting a measurement variable, comprising: a scintillator for generating light pulses, a plurality of optoelectronic sensors, wherein a respective optoelectronic sensor is embodied to convert the light pulses generated by the scintillator into an associated sensor signal; and an evaluation unit, comprising an assessment part, wherein the assessment part is embodied to assess a respective sensor signal as an error-free or erroneous sensor signal, and a summation part, wherein the summation part is embodied to form a summed sensor signal of the error-free sensor signals for the purposes of obtaining a measurement variable signal for the measurement variable.
The radiometric detector according to the invention for detecting a measurement variable has a scintillator for generating light pulses in a manner dependent on an incidence of ionizing radiation, wherein the radiation incidence is dependent on the measurement variable. In detail, the scintillator of the radiometric detector is excited when ionizing radiation passes through and it reemits the excitation energy in the form of light pulses. In particular, the scintillator can be a scintillation crystal.
Moreover, the radiometric detector has a plurality of optoelectronic sensors, wherein an optoelectronic sensor is embodied in each case to convert the light pulses generated by the scintillator into an associated electrical sensor signal. Hence, a plurality of sensor signals are generated. The sensor signals from the optoelectronic sensors are correlated in time since the scintillation light generated in the scintillator is distributed over all (or at least a multiplicity) of the optoelectronic sensors. The plurality of optoelectronic sensors are optically coupled to the scintillator; in particular, the optoelectronic sensors can be attached to the scintillator. The optoelectronic sensors can each have dedicated readout electronics, wherein the electrical sensor signals are formed and amplified in one of the readout electronics in each case. In particular, the optoelectronic sensors can be photomultipliers (electron tubes), photodiodes or silicon photomultipliers (SiPMs).
Moreover, the radiometric detector has an evaluation unit, wherein the respective sensor signals of the plurality of optoelectronic sensors are applied to the evaluation unit. The evaluation unit has an assessment part and a summation part. The assessment part is embodied to assess a respective sensor signal from the plurality of sensor signals as an error-free or erroneous sensor signal. Typically, a possible error or failure of one of the optoelectronic sensors causes a corresponding erroneous sensor signal. Hence, the assessment part can identify a possible error or failure of one of the optoelectronic sensors by assessing the respective sensor signals.
The summation part is embodied to form a summed sensor signal, preferably only, from only the error-free sensor signals for the purposes of obtaining a measurement variable signal for the measurement variable. Therefore, the individual sensor signals are evaluated in parallel. In the worst case, all sensor signals are assessed as erroneous sensor signals. No summed sensor signal is formed in that case. If the radiometric detector is fully functional, i.e. none of the optoelectronic sensors are faulty or failed and all sensor signals are assessed as error-free sensor signals, the best signal-to-noise ratio (S/N) is obtained by adding the time-correlated analogue sensor signals. This can be explained by virtue of the sensor signals being correlated in time (gamma event in the scintillator), but noise in each one of the individual optoelectronic sensors being temporally independent of the other sensors. Therefore, the sensor signals are processed in such a way that there are significant advantages and, in the worst case, no losses in the signal-to-noise ratio in relation to a single-sensor measurement system; i.e., there are no disadvantages from a metrological point of view.
The optoelectronic sensors therefore have an internally redundant embodiment. Typically, these have a higher failure probability than other components of the radiometric detector. Moreover, a voltage supply of the optoelectronic sensors can have a redundant and independent design. In the case of suitable mechanical encapsulation, the scintillator has a very low failure probability. Therefore, the radiometric detector can still establish a reliable summed sensor signal or a reliable measurement variable, even in the case of single sensor or multiple sensor failures. This increases the availability and reliability of the radiometric detector or the measurement and improves the characteristics within the scope of a functional safety consideration pursuant to SIL (safety integrity level). Since this is carried out in a single radiometric detector instead of by virtue of operating a plurality of radiometric measurement systems, this leads to significant savings for a customer during procurement, installation, operation and servicing of the radiometric detector. Moreover, the radiometric detector according to the invention saves space in relation to a plurality of radiometric measurement systems. This is advantageous in many applications, such as e.g. in the case of continuous casting in steelworks, in which the required space and the necessary power supply are likewise a limiting factor. The problem of a redundant radiometric detector lies in finding a compromise between granularity (degree of redundancy) and the best signal behaviour (formation of the analogue sum for highest S/N). The detector architecture presented here comprehensively enables both. Moreover, this is a particularly cost-effective variant as a result of using a single scintillator.
Alternatively, the radiometric detector according to the invention can have a multiplicity of scintillators arranged adjacent to one another, wherein at least one optoelectronic sensor is optically coupled to each scintillator. Each one of the plurality of scintillators with the at least one optoelectronic sensor can be referred to as a scintillation module. A plurality of these mutually independent scintillation modules are arranged packed together as closely as possible.
As described above, the assessment part in this variant is also embodied to assess a respective sensor signal from the plurality of sensor signals as error-free or erroneous sensor signal. In this case, the summation part is embodied to form individual summed sensor signals only from the error-free analogue sensor signals of the individual scintillation modules in each case and to form a summed sensor signal from the individual summed sensor signals or signals formed by further processing thereof for the purposes of obtaining a measurement variable signal for the measurement variable. As a result of an optical separation of the scintillation modules from one another, a time correlation between the analogue sensor signals from optoelectronic sensors of two different modules is only to be expected in the case of Compton scattering. The generated scintillation light or the generated light pulse remains within one scintillator and it is captured by the at least one optoelectronic sensor. Sensor signals not correlated in time may not be added in analogue form since this would otherwise reduce the S/N. All sensor signals or individual summed sensor signals are—at least averaged over time—linked linearly to one another if the radiometric detector is irradiated in a homogeneous fashion.
The use of a plurality of individual scintillators makes this variant more expensive but, on the other hand, increases the reliability of the radiometric detector since, for example, a break in the scintillator only affects the single scintillation module and the corresponding sensor signals.
In an embodiment of the invention, the scintillator, the plurality of optoelectronic sensors and the evaluation unit are arranged in a common housing. A customer or a user therefore receives a single device or a single object.
In an embodiment of the invention, the assessment part has a voting logic, such as a 1oo2 voting logic, wherein the voting logic is embodied to assess a respective sensor signal from the plurality of sensor signals as an error-free or erroneous sensor signal. A voting logic identifies errors or failures particularly well and quickly.
In an embodiment of the invention, the plurality of optoelectronic sensors has at least three optoelectronic sensors and the voting logic is embodied to compare the plurality of sensor signals to one another and to assess a respective sensor signal from the plurality of sensor signals as an error-free or erroneous sensor signal depending on the comparison result. In particular, this can be a 2oo3 voting logic. If the radiometric detector is fully functional, i.e. none of the optoelectronic sensors are faulty or failed, all sensor signals are—at least averaged over time, e.g. over 60 seconds—linearly linked to one another if the radiometric detector is irradiated in a homogeneous fashion. By way of example, if the fill level in a container drops, all (mean) sensor signals must increase by the same factor. If this is not the case and if deviations, e.g. by more than 10%, of one optoelectronic sensor from the other optoelectronic sensors are determined by comparing the sensor signals with each other, this indicates a malfunction or failure of the corresponding sensor or the corresponding scintillator. The corresponding sensor signal is then assessed as an erroneous sensor signal.
In an embodiment of the invention, the summation part has a switching element and a summation element. The switching element has a signal connection with the assessment part and it is embodied to forward a respective error-free sensor signal and not to forward a respective erroneous sensor signal. Forwarding or not forwarding a respective sensor signal can be carried out by appropriate switching states of switches of the switching element in a manner depending on the assessment of the assessment part. This renders it possible to mask an erroneous sensor signal from the summed sensor signal formation. The summation element is embodied to form the summed sensor signal from the error-free sensor signals forwarded by the switching element. As an alternative or in addition to the switching element, the summation part can have a correlator for signal processing.
In an embodiment of the invention, the evaluation unit has a comparator and a counter. The comparator is embodied to compare the summed sensor signal, or a signal formed by further processing of the summed sensor signal, with a measurement threshold and to generate an output signal depending on a comparison result. The comparator analyses the summed sensor signal or the signal formed by further processing of the summed sensor signal in terms of the height thereof. The output signal is generated if the signal height exceeds the measurement threshold. The counter is embodied to register the output signal and to generate a count rate signal for the purposes of obtaining the measurement variable signal for the measurement variable, wherein the count rate signal is a number of registered output signals per unit time. The count rate signal contains information about the measurement variable or process variable.
In an embodiment of the invention, the radiometric detector has an analogue-to-digital converter. The analogue-to-digital converter is embodied to digitize a respective sensor signal or the summed sensor signal or a signal formed by further processing of the summed sensor signal. In particular, the analogue-to-digital converter can be a constituent of the evaluation unit. The further procedure is then carried out digitally in the manner as described hereabove and herebelow. When digitizing the summed sensor signal by means of the analogue-to-digital converter, the comparator can be dispensed with if necessary. The evaluation unit, the analogue-to-digital converter, the assessment part, the summation part and/or the comparator can be realized in the form of a microprocessor and associated software.
Moreover, the evaluation unit can advantageously have a conversion part, wherein the conversion part is embodied to convert or transform the summed sensor signal or a signal formed by further processing of the summed sensor signal, such as the count rate signal, into the measurement variable signal for the measurement variable or process variable. In particular, to this end, conversion or transformation functions can be stored in the conversion part.
In an embodiment of the invention, the evaluation unit has a compensation part, wherein the compensation part has a signal connection with the assessment part. The compensation part is embodied to compensate a number of erroneous sensor signals during further processing of the summed sensor signal for the purposes of obtaining the measurement variable signal for the measurement variable. Here, the compensation part can advantageously be embodied to take into account an overall number of the plurality of optoelectronic sensors and hence of the sensor signals. By not taking into account an erroneous sensor signal, the latter is missing in the summed sensor signal, as a result of which an incorrect measurement variable signal may be caused. In the case of a specific number of erroneous sensor signals and a specific number of error-free sensor signals, the summed sensor signal can be reduced by a factor of number of error-free signals/overall number of the sensor signals (number of erroneous sensor signals plus number of error-free sensor signals) in relation to an expected summed sensor signal in the case of a fully functional detector. In particular, the height of the summed sensor signal or of a signal formed by further processing of the summed sensor signal may be so low that the signal level is no longer sufficient to exceed the measurement threshold of the counter. This then causes the count rate signal to equal zero. Advantageously, this is compensated for by the compensation part.
In an embodiment of the invention, the compensation part has an amplifier with an adjustable gain factor, wherein the amplifier has a signal connection with the assessment part. The amplifier is embodied to set the gain factor in a manner dependent on a number of error-free sensor signals and the number of erroneous sensor signals. Moreover, the amplifier is embodied to amplify the summed sensor signal with the gain factor for generating an amplified summed sensor signal or to attenuate the measurement threshold by the gain factor. Hence, the amplifier can compensate an erroneous sensor signal not considered when forming the summed sensor signal. In the case of a specific number of erroneous sensor signals and specific number of error-free sensor signals, the gain factor for amplifying the summed sensor signal is overall number of sensor signals/number of error-free signals. As a result, the height of the amplified summed sensor signal corresponds to an expected height of the summed sensor signal when there is no erroneous sensor signal in the radiometric detector. Additionally or alternatively, the measurement threshold of the comparator can advantageously be adjustable. Then, the gain factor for attenuating the measurement threshold is number of error-free signals/overall number of sensor signals. As a result, the summed sensor signal can exceed the attenuated measurement threshold and lead to the generation of an output signal.
In an embodiment of the invention, the radiometric detector has a malfunction output unit. The malfunction output unit has a signal connection with the assessment part and it is embodied to output a malfunction signal in the case of an erroneous sensor signal. The faulty behaviour or a failure of an individual optoelectronic sensor or a scintillator can be communicated immediately to a user or operator by means of the malfunction signal. Hence, servicing or repair of the affected component can take place before further components fail and hence the whole radiometric detector is no longer functional. In particular, the malfunction signal can contain information about the component that is faulty or failed. The malfunction signal can be output in acoustic form by means of a loudspeaker of the malfunction output unit, in optical form by means of at least one warning lamp of the malfunction output unit and/or in the form of an electronic communication to a control system for the radiometric detector or to a control centre.
Moreover, the radiometric detector can advantageously have a transmission part, wherein the transmission part is embodied to transmit the summed sensor signal or a signal formed by further processing of the summed sensor signal, such as the count rate signal or the measurement variable signal for the measurement variable or process variable, to an external device, for example in a control centre. In particular, the transmission part can be a modem or a signal transducer. For transmission purposes, use can be made of a bus system such as HART, Profibus, Modbus or EROA based on various physical carriers such as 4-20 mA, RS485 or FSK.
The respective constituents of the evaluation unit and also of the transmission part and all components required herefor, to the extent that they are present, have a failure risk which, in the most disadvantageous case, would lead to the transmission of an incorrect signal from the radiometric detector to e.g. a control centre.
In an embodiment of the invention, the radiometric detector has a further optoelectronic sensor, a comparison part and a further malfunction output unit. The further optoelectronic sensor is embodied to convert the light pulses generated by the scintillator into an associated further sensor signal. The comparison part is embodied to compare, in particular continuously, a further measurement variable signal formed by further processing of the further sensor signal with the measurement variable signal. Advantageously, the further measurement variable signal and the measurement variable signal can be applied to the comparison part. The further malfunction output unit is embodied to output a malfunction signal depending on a comparison result, for example in the case of a deviation of the further measurement variable signal from the measurement variable signal. In particular, the further malfunction output unit can have a signal connection with the comparison part. In particular, the further sensor signal of the further optoelectronic sensor may not be applied to the evaluation unit, to which the respective sensor signals of the plurality of optoelectronic sensors are applied. Instead, the radiometric detector can have a further evaluation unit for further processing of the further sensor signal to form the further measurement variable signal, wherein the further sensor signal from the further optoelectronic sensor may be applied to the further evaluation unit. Therefore, separate, further or completely independent signal generation and signal processing may take place. As a result of this, the comparison part can identify a possible fault or failure of the respective constituents of the evaluation unit, of the transmission part and/or of all components required herefor, to the extent that these are present, and it can output the malfunction signal by means of the further malfunction output unit, in particular communicate said malfunction signal to a user or operator. In particular, the malfunction signal may contain the information as to which part is faulty or failed. The malfunction signal can be output in acoustic form by means of a loudspeaker of the further malfunction output unit, in optical form by means of at least one warning lamp of the further malfunction output unit and/or in the form of an electronic communication to a control system for the radiometric detector or a control centre. Moreover, a transmission of the measurement variable signal from the radiometric detector to the outside can be interrupted in the case of a malfunction, for example by opening a switch of the radiometric detector.
In an embodiment of the invention, the measurement variable is a filling level or a moisture content or a density or a mass flow.